Yes, many of us know that Wherefore is Why. That doesn’t change the fact that 99% of English speakers think it means Where. When the vast majority of a population thinks a word means something different, then the word MEANS something different. It is one of the basic rules of language evolution. It makes the line in the play make less sense, but that doesn’t change the common perception of the word.

This doesn’t work retroactively. If “infamy” ever becomes a good thing due to common perception, that doesn’t mean that Roosevelt meant something different when he called December 7, 1941 “A date which will live in infamy.”